wonderings

Well, in principle you just start with a full grid and remove a bunch of numbers. Of course, you need your remaining numbers to give a unique solution... but that's not necessarily as difficult as running through the puzzle to check. It would depend in part on how many numbers you take out on the grid.

How do you get the full grid, though? If you just start writing numbers in a blank Sudoku grid, won't you quickly just create a Sudoku with no real solution? You've probably got to work out really complex relationships between squares. Though I guess it might be easier if you placed all nine of each digit at once. Actually, that might make it really easy. I'm not sure I don't think I thought of that in my vague half-memory of maybe I tried to create a Sudoku once.